1. Field of the Invention
New detection methods for immunoassays which allow the assays to be performed rapidly with a minimum amount of equipment and operator time have been recently reported. In several of these procedures, immune complexes are identified directly, without the use of fluorescent, radiochemical or enzyme labeling methods. These label-independent methods detect immune complex formation based on electrochemistry (Electrochemical Sensors in Immunological Analysis, Ngo, TT ed. Plenum Press, NY N.Y. USA), ellipsometry (J. Colloid Interface Sci. 111:544-554, 1986), optical wave guidance (Sensors Actuators B1:592-596, 1990), surface plasmon resonance (Biosensors 3:211-225, 1988, Z. Phys. 4:299-304, 1983; Biotechniques 11:620-627, 1991), and the piezoelectric effect (Biosensors Bioelectron 5:13-26, 1990; Anal. Chem. Acta 271:111-121, 1989; Anal. Chem. 55:2333-2386, 1983; Science 249:1000-1007, 1990). In spite of obvious advantages for rapid, label-independent biospecific analysis, all of the procedures share the disadvantage of requiring immobilized antibody or antigen. Conventional procedures for preparing such immunoreactive surfaces are not optimal, and newer methods for coupling antibody to solid surfaces have been reported (Ann.N.Y. Acad. Sci. 613:391-395; 439-443, 1990).
2. Description of Related Art
Coating techniques currently in use to prepare immunoreactive surfaces include entrapment of the antibody onto a polymer coated surface (Biotech Letts 8:643-648, 1986), glutaraldehyde crosslinking of antibody onto surfaces (J. Biomed. Mater. Res. 6:565-570, 1970, Clin. Chem. 30:1533-1538, 1984), absorption of antibody onto silanated surfaces (Anal. Chem. 55:2333-2336, 1983), and attachment of antibody to immobilized protein A (Anal. Chem. 59:2760, 1987). These methods, however, generally have the common drawback that each antibody coated surface can be used only a limited number of times before immunoreactivity is lost (see, e.g., Anal. Lett. 24:1283-1292, 1991; Biotechnology 7:349-351, 1989; Ann. N.Y. Acad. Sci. 613:439-443, 1990).